1. Field of the Invention
The present invention relates to a multi charged particle beam writing apparatus and a multi charged particle beam writing method. More specifically, for example, the present invention relates to a method for reducing the time of writing with multiple beams.
2. Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in the semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. The electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” a pattern on a wafer and the like with electron beams.
In a variable shaped beam (VSB) type electron beam writing that uses a single electron beam for writing, the more patterns become complicated, the more it becomes necessary to divide patterns into fine shot figures, so that the writing time becomes long. In order to solve this problem, it could be thought to shorten the writing time by increasing a beam current density so as to compensate the increase in the number of shots. However, if this method is employed, since the influence of resist heating and the like becomes large, there is a limit also to this method.
Now, think of a writing apparatus using multiple beams (multi-beams). Compared with the case of writing a pattern by using a single electron beam, since it is possible to emit multiple beams at a time in multiple writing, the throughput can be greatly increased. In a writing apparatus employing a multi-beam system, for example, multiple beams are formed by letting an electron beam emitted from an electron gun assembly pass through a mask with a plurality of holes arranged in a matrix, blanking control is performed for each of the multiple beams, and each unblocked beam is deflected by a deflector to irradiate a desired position on a target object or “sample” (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2006-261342). In the writing apparatus of this multi-beam system, since a plurality of beams are emitted at a time, the influence of pattern shapes on the writing time is small compared with a variable shaped beam system.
The writing time is affected not only by a pattern shape but also by a pattern density, for example. In the variable shaped beam type electron beam writing described above, it is sufficient to emit beams only to a point where a pattern exists. In other words, it is sufficient to pass through a point where a pattern does not exist, without emitting beams. Therefore, the writing time is short in the case of layout with low pattern density. By contrast, the writing time is long in the case of layout with high pattern density. On the other hand, in the multi-beam writing, it is thought that since a plurality of beams are emitted at a time, the higher the layout pattern density is, the shorter the writing time becomes compared with the variable shaped beam type electron beam writing. However, the lower the layout pattern density is, the larger the dose needed for exposure becomes. Therefore, consequently, in the multi-beam writing, the lower the layout pattern density on the whole is, the longer the writing time becomes compared with the case of high layout pattern density on the whole. For example, when writing the layout of a line and space pattern whose pattern density is 10% with multiple beams, it needs 1.5 times the writing time of writing the layout of a line and space pattern whose pattern density is 50% with multiple beams. Accordingly, in the multi-beam writing, it is requested to further reduce the writing time. Particularly, reducing the writing time while mitigating the influence of a pattern density is requested.